The present invention relates to a data transfer device and method thereof.
In the display device made available in recent years, such as a Liquid Crystal Display (LCD) or the like, pixel data for representing an image has been treated not in an analog system but in a digital system. Especially with recent improvement on performance, there has been an increase in the quantity of data to be transferred.
When data transfer is performed through a bus in the digital system, in order to deal with the increased quantity of data, the number of signal lines constituting the bus must be increased unless a frequency is increased. Consequently, the bus is enlarged. Thus, if the frequency of data transfer is set high, radiation of an electromagnetic wave, i.e., Electro-Magnetic Interference (hereinafter referred to as EMI,) or the like occurs when data (digital signals of “1”: high, and “0”: low) flows through the signal lines.
The EMI occurs when transferring data, which differs from data, transferred immediately therebefore (data is changed from high to low, or from low to high), and characteristically becomes more conspicuous as the number of data to be changed is increased.
Therefore, the background art has presented methods of inverting data in a case where data changes at a predetermined number or more of signal lines constituting the bus. One of the examples is a method disclosed in Japanese Patent Laid-Open Hei 4 (1992)-303234.
According to such a method, if “data to be transferred” (hereinafter referred to as Transferring Data) differs from “data transferred immediately before” (hereinafter referred to as Proximate Data) at a half or more of the number of signal lines constituting the bus, this Transferring Data is inverted (to low when data is high, and to high when data is low). Specifically, when inverting, the data changing style in which the data is changed from low to high (from high to low) becomes the style in which the data is changed from high to high (from low to low), thus no changes occur. The data changing style before inverting, in which the data is changed from high to high (from low to low) becomes the style, in which the data is changed from high to low (from low to high). Thus, by inverting the Transferring Data, the number of data to be changed is reduced for all the signal lines constituting the bus, and the EMI or the like is thereby suppressed.
When the data is inverted in the foregoing manner, a signal indicating the execution of inversion (hereinafter referred to as an inversion bit) is simultaneously transferred from a transmission side. This inversion bit is transferred by allocating one of the signal lines constituting the bus thereto. For example, a signal “0” is transferred when no data inversion is performed, and a signal “1” when inversion is carried out. At a receiving side, when the data and the inversion bit are received, the data is returned to the state before the inversion, and then subjected to predetermined processing.
According to the foregoing technology of the conventional art, for example, if the Transferring Data through the bus is all changed, it is possible to greatly reduce the total number of data to be changed through all the signal lines constituting the bus by inverting the data.
As an example, assuming that a half or more of the number of Transferring Data the bus is changed, the data is inverted. However, a difference in states between before and after the inversion may be small, and the advantage of suppressing EMI, obtained by the inversion, may also be limited. Therefore, in the technology of the conventional art, the suppression of EMI by the data inversion cannot always be effective.
Such a problem is not limited to the transfer of pixel data at the display device, but common to the transfer of data through the bus or the like, especially when the number of data bits to be transferred in synchronization is large.